1. Field of the Invention
The present invention relates to a valve device for a refrigerating cycle, in particular, a valve device using an aluminum alloy material excellent in intergranular corrosion resistance.
2. Prior Art
A valve device such as a solenoid controlled valve and a thermostatic expansion valve has been used for a refrigerating cycle of, for example, a vehicle air conditioner. The valve device conventionally has a main body mainly made of an aluminum alloy material.
As the aluminum alloy material used for the valve main body, a JIS 6262 alloy extruded material has been used due to its secured machinability. However, this material needs to undergo an alumite treatment in order to increase its corrosion resistance for using such a purpose, which has caused a problem of a high production cost.
In order to eliminate the alumite treatment, a JIS 6063 alloy excellent in corrosion resistance and machinability can be used for the valve device instead of the 6262 alloy poor in corrosion resistance. However, in case that the valve device, for example a thermostatic expansion valve, using the 6063 alloy is provided in an engine room having a sever corrosive environment with the valve combined with a member of dissimilar metal such as stainless and brass, there is a possibility that an electrolytic corrosion due to a potential difference between the 6063 alloy and the dissimilar metal causes an intergranular corrosion in the 6063 alloy, which is rarely caused in the 6063 alloy in a usual case. That is, corrosion occurs on grain boundaries in preference to the other parts of the alloy. When such an intergranular corrosion occurs on an inner surface layer of refrigerant passages and the like formed in the thermostatic expansion valve, the crystal grains in the corroded surface layer are likely to be loosened and finally separated from the surface layer. With increase in the corrosion loss, the original surface layer breaks away to give a leakage pass through which the refrigerant leaks from the refrigerant passages. Therefore, it has been desired to prevent the problem of refrigerant leakage by suppressing the intergranular corrosion of the aluminum alloy material.
The present invention has been made in light of the above-mentioned problem and it is accordingly an object of the present invention to provide a valve device having substantially no or an extremely decreased refrigerant leakage by using an aluminum alloy material excellent in intergranular corrosion resistance without an alumite treatment.
According to the present invention, provided can be a valve device including a main body formed with a passage for allowing a refrigerant to flow therethrough; and a valve member provided in the passage. The main body includes an aluminum alloy containing 0.2 to 1.5 weight % of Si; 0.2 to 1.5 weight % of Mg; 0.001 to 0.2 weight % Ti; at least 0.1 weight % of Mn, Zr or the both; and Al and inevitable impurities. The aluminum alloy material has a fiber structure.
It is preferred that the maximum contents of Mn and Zr contained in the aluminum alloy material are respectively 1.0 weight % and 0.5 weight %.
The valve device may be a thermostatic expansion valve or a solenoid controlled valve. In case of the thermostatic expansion valve, the main body is formed with a first passage for a liquid-phase refrigerant; a second passage for a vapor-phase refrigerant obtained by vaporizing of the liquid-phase refrigerant; and an orifice provided in the first passage and adapted for adiabatically expanding the liquid-phase refrigerant, and the valve member is provided near the orifice.
It is preferred that each crystal grain of the aluminum alloy material has an aspect ratio (a grain length/a grain thickness) of 10 or more.
The refrigerant passage may have an inner surface substantially parallel to a fiber direction of the fiber structure. A fiber direction means an elongated direction (i.e., a direction of the grain length) of the crystal grains constituting the fiber structure.
The aluminum alloy material is preferably an extruded material. In this case, an aluminum alloy ingot may be homogenized at 450 to 550xc2x0 C. before the extrusion. In the extrusion of the ingot, preferable extrusion temperature and extrusion rate are respectively 470 to 550xc2x0 C. and less than 40 m/min.